Solution-Processed Metal Ion Polyelectrolytes as Hole Transport Materials for Efficient Inverted Perovskite Solar Cells

Despite achieving high efficiencies over a short time, further streamlining of hybrid lead-halide perovskite solar cell (PSC) designs is necessary for their commercial viability. In this contribution, a new class of interfacial hole transporting layer (HTL) materials consisting of anionic polyelectrolytes comprising polystyrene sulfonate (PSS) with metal cations are explored. These materials represent alternatives to metal oxides, combining characteristics of metal oxides with the facile preparation and desirable film-forming characteristics of polyelectrolytes. Polyelectrolytes with cations including Li, Mg, V, Mn, Co, Ni, Cu, Zn, Pd, Ag, In, Cs, and Pb as HTLs in inverted PSCs are explored. A range of positive and negative effects is observed for different metal cations, which are attributed to differences in the physical properties of the polyelectrolytes, and their influence on the electronic band structure of devices and the crystal qualities of the perovskite absorber. Ni and Cu polyelectrolytes created p-type contacts at the anode of PSCs, improving device performance. These materials are believed to have potential in other types of devices as well. This type of metal:PSS polyelectrolyte has not yet been widely investigated, however, it is shown that it constitutes a simple and economic strategy to engineer energy band structures in perovskite devices.